The Fauna of the River Teifi, West Wales

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Abstract
The river Teifi has suffered little or no pollution of any kind and possesses a rich fauna and flora. The mainstream, from its source to its estuary, measures about 80 miles and varies to a very great extent in gradient. Near its source the stream has a gradient of over 350 ft. per mile; in the region of the Tregaron bog the river consists of a series of stagnant pools and has a gradient of < 2 ft. per mile. Tributaries are numerous, and the river is subject to heavy floods. The river water is soft and slightly less acid than that of the rivers Rheidol, Ystwyth and Dovey. The fauna list includes some 147 spp., the majority being Arthropoda. The fauna is very variable, ranging from a purely lotic type in the upper reaches of the river to a purely lentic type in the Tregaron bog region, while the middle and lower reaches have both types of fauna represented. The river provides excellent fishing for salmon, sea-trout and trout, but no coarse fish are caught. The fauna of the lower reaches of the Teifi is compared with that of the lower reaches of the Rheidol, a river which has become repopu-lated after many years of barrenness due to the pollution by Pb and Zn. The fauna of the lower reaches of the Teifi is virtually limited to spp. generally found in flowing water; that of the lower reaches of the Rheidol includes several spp. most usually found in stagnant waters. This would suggest that when the Rheidol became repopulated, some of the spp. composing its present fauna were recruited from the pools in its valley.